How do I create slices of a topographical mesh?
Create a plane that is larger than your terrain and create an array in the Z direction. Add a Boolean modifier to the terrain - the plane is used as a cutter. Visually you can create the layers by then adding a solidify modifier...



...but you asked about creating curves so - apply the Boolean and then in Edit mode press P and choose by loose parts. Back in Object mode while all the objects are still selected press ALTC and convert your meshes to curves.